1. Field of the Invention
The present invention relates to apparatus for the treatment of a semiconductor wafer. More particularly, the present invention relates to apparatus for effectively forming an oxide membrane on a semiconductor wafer.
2. Description of the Prior Art
Semiconductor devices such as transistors and integrated circuits have been prepared by various treatments for the semiconductor wafers. The treatments include a treatment for forming a silicon oxide membrane on the surface of the semiconductor wafer, such as a silicon wafer, by heat oxidation, and also include a gaseous diffusion method for diffusing an impurity into the semiconductor wafer by contacting it with a gas containing the impurity under the condition of heating the semiconductor wafer. The heat oxidation treatment of the silicon wafers is usually conducted by heating the silicon wafers at about 1000.degree. C under the condition disposing the silicon wafers in an oxidizing gas.
An undesirably long time is necessary in order to form the silicon oxide membrane on the surface of the silicon wafer by the heat oxidation treatment. For example, it usually takes about 10 hours to form a silicon oxide membrane having a thickness of 1 - 2 .mu. m.
In the gaseous diffusion treatment, it also takes an undesirably long time for the heat treatment in order to provide a high concentration of the diffused impurity. Thus, the undesirably long heat treatment causes the spreading of various diffused regions formed in the wafer to an undesirable extent whereby the electrical characteristics of the semiconductor device are detrimentally effected.
An apparatus for the heat-treatment of a silicon wafer in an oxidizing gas compressed at about 10 atm. has been proposed for shortening the treatment time in the heat oxidizing process. When this apparatus is used, the formation of a silicon oxide membrane is promoted, for example, in order to shorten the time for forming the silicon oxide membrane having a thickness of 1.5 .mu. m to about 1 hour.
This apparatus can be used for the gaseous diffusion treatment while compressing the gas containing the impurity. In this case, the diffusion of the impurity into the wafer can be done under the formation of the silicon oxide membrane.
However, in the above-mentioned apparatus, the wafers and the heater for heating the wafers are disposed in the same chamber with the result that the compressed gas which is charged into the chamber contacts both the wafers and the heater. In this case, the semiconductor wafers are contaminated with various impurities vaporized from the heater through the compressed gas with the result that the electrical characteristics of the semiconductor device are disadvantageously deteriorated.
It is preferable to prepare the chamber with a material which does not vaporize an impurity for contaminating the wafers such as quartz so as to prevent the contamination caused by the material of the chamber. However, in the above-mentioned apparatus, the pressure difference between the outer pressure and the inner pressure of the chamber is too high. Accordingly, it is difficult to form the chamber of the apparatus with quartz which has a rather low mechanical strength under the pressure.